PROJECT SUMMARY/ABSTRACT For early diagnosis to lead to early intervention, our diagnostic tools need to provide affordable, accessible, and accurate tests of auditory function in any healthcare setting. As it is, distortion-product otoacoustic emission (DPOAE) testing provides an objective and noninvasive measure for evaluating the health of a common site of age-related declines in the auditory system ? the outer hair cells. DPOAEs are a familiar tool due to their widespread use in newborn hearing screening and other audiological clinical applications. We contend that the test performance of DPOAEs can be improved significantly by aligning the methods to evoke them with known, place-specific mechanical properties of the mammalian cochlea. Currently utilized DPOAE measurement protocols are not optimized to detect dysfunction across the entire cochlea, especially those common age-related conditions that first manifest at the very base. Recent advances in calibration techniques and measurement hardware allows for delivery and recording of accurate emission levels up to 20 kHz [14-15]. This proposal tackles the remaining important step by developing a DPOAE test protocol guided by local cochlear mechanical properties and evaluating its test performance. We will use state-of-the art techniques for calibrating the stimulus pressure [64-65] and correcting the DPOAE pressure [45] to compensate for individual variations in ear canal anatomy while concurrently delivering stimuli and recording DPOAEs. The stimulus frequency ratio and stimulus levels will be adjusted in a frequency- specific manner to maximize DPOAE generation and improve test performance for both screening for hearing loss and predicting hearing thresholds. We hypothesize that DPOAE stimulus parameters that are optimized for the cochlear place of stimulation will evoke emissions that accurately reflect cochlear health and therefore will be closely related to behavioral hearing thresholds. We plan to pursue the following aims: (1) Develop a novel DPOAE measurement protocol optimized to local cochlear mechanical properties, (2) Evaluate the novel DPOAE measurement protocol in detecting the presence of hearing loss, and (3) Apply the novel DPOAE measurement protocol for the prediction of hearing thresholds. Through detailed investigation of physiologically derived characteristics of DPOAEs in young, normal-hearing adults, we expect that DPOAE amplitudes will be significantly correlated with behavioral hearing thresholds in normal-hearing and hearing-impaired individuals. This proposal leverages the latest developments in calibration and measurement hardware to develop a DPOAE measurement system that is optimized for local cochlear properties. These optimizations are expected to improve DPOAE test performance significantly positioning the new test as an important, affordable, and accessible tool for early detection of age-related cochlear function. The clinical implications are significant as we propose to improve a well-accepted clinical tool that can easily be automated for widespread deployment.